Patent GB-191219251-A (GB)
Title: Improvements in or relating to Telephone Systems.
Filed: 1912-08-22
Granted: 1913-08-22
Abstract: 19,251. Automatic Telephone Manufacturing Co., [Automatic Electric Co.]. Aug. 22. Semi-automatic exchange systems.-A system is described in which answering and calling cords at private branch exchanges are interconnected through a main exchange by automatic Strowger switches, which may be controlled either by the calling subscriber or by the operator in charge of the answering cord. In Figs. 1, 2, 3, and 4, which should be assembled side by side, the means are shown by which connexion is established between a subscriber A, Fig. 1, belonging to an automatic private branch exchange having switches C, E, F organized on the two-wire principle, and a subscriber A<1>, Fig. 4, belonging to a second private branch exchange which is not itself provided with automatic switches although the subscribers are furnished with impulse - sending devices. The main exchange is equipped with switches H, I, N, Fig. 3, organized on the three-wire principle, and the impulse-senders of the subscribers A<1> arc of the sort required for operating switches of that kind. The subscriber A is first connected by an operator's cord-circuit O to a local two-wire selector C, and impulses representing the number of a cord O<1> at the exchange of the subscriber A<1> are then transmitted either by the subscriber A or by the operator in charge of the cord O. The selector C extends the connexion to a trunk line 167, 168, Fig. 2, terminating in a second selector H of the main exchange. The switches at this exchange being of the three-wire type, a repeater D, Fig. 2, is provided in the outgoing end of the trunk 167, 168 to translate the current-interruptions in the circuit 155, 156 into earth return currents over the two trunk wires. The connexion is further extended by the three-wire selector H and connector I to a trunk 230, 231 ending in a cord-circuit 0' at the branch exchange of the wanted subscriber, who is rung up by the operator in charge of the cord O<1>. If the subscriber A wishes to call the subscriber A, the connexion is made over the same trunk 230, 231, but through the selector N at the main exchange and the selector F and connector E at the automatic branch exchange. A repeater M in this case translates the impulses in a reverse sense to that indicated above. It will be seen that the lines of the branch exchange subscribers terminate only in jacks, and that connexion with them is made in every case through a cord. The ringing is controlled by the B operator, but the automatic switches are released by the calling subscriber. A fuller description of the two connexions is given below. Connexion of subscriber A, Fig. 1, to subscriber A<1>, Fig. 4; signalling the operator in charge of the cord O. When the subscriber A lifts down his receiver, a circuit is closed through the call lamp 102 over the line wires 100, 101. The operator plugs a cord O belonging to a first selector C into the jack J, opening the circuit of the lamp 102 at the jacksprings 104, 106, and operates the key K<1> to connect her instruments S to the calling line to ascertain the wanted number. The necessary impulses, consisting, for each digit, of a rapid series of interruptions of the two-wire circuit 112, 148, are then transmitted either by the subscriber or by the operator, the key K being thrown in the latter case to connect the impulse-sender 149 and instruments S across the trunk 112, 148 of the first selector C. If the operator should take charge of the selecting- operations, a relay 42 is energized when the key K<1> is thrown, and if the calling subscriber should hang up his receiver while the selecting operations are in progress, the upper winding of the relay 42 is bridged across the cord O, thus preventing the automatic switches from being released when the key K<1> is eventually restored. The relay 42 is unlocked by the energization of the supervisory relay 38 when the subscriber again lifts down his receiver. The number called is that which represents the trunk cord O<1>, Fig. 4, of an operator at the exchange of the wanted subscriber A<1>. Operation of the two-wire first selector C, Fig. 1. As soon as the plug P was inserted in the jack J, the selector line relay 56 was energized over the calling line and closed a circuit through the slow-release relay 62. This, among other effects, puts a guarding ground-potential on the test terminals 141, Fig. 2, belonging to the cord O in the banks of the connectors E. The current-interruptions representing the first digit de-energize the relay 56, closing a circuit through the slow-release private-magnet relay 63, which energizes the private magnet 55, and through the vertical magnet 49, which lifts the wipers 46, 47, 48 to the desired level. When the last impulse has passed, the relay 63 and private magnet 55 de-energize, and the side switch moves to its second position. The selfinterrupting rotary magnet 50 is now connected in over the side switch arm 54 and rotates the wipers 46, &c., over the bank terminals until an idle trunk 1.67, 168, Fig. 2, is reached, whereupon the side-switch moves in known manner into the third position, cutting out the rotary magnet 50 and line relay 56 and extending the trunk wires 112, 148 to the wipers 46, 47. The de-energizing of the line relay 56 opens the circuit of the relay 62, but before this relay has time to fall back it is provided with a fresh circuit over the test-wiper 48 by the energization of the relays 74, 77, Fig. 2, belonging to the repeater D. This circuit also provides a guarding ground-potential for the test-terminals 176, Fig. 1. Operation of the two-wire-to-three-wire repeater D, Fig. 2. The current interruptions representing the second and each subsequent digit are translated by the repeater D into a series of ground-impulses over the ' vertical ' trunk wire 167, followed by a single ground impulse over the ' rotary ' trunk wire 168. Each interruption de-energizes the relay 74 and closes a circuit from ground G<6>, through a back contact of the relay 74 and a front contact of the relay 77 (which, being a slow-release relay, remains energized throughout) to the trunk wire 167. A slow - release relay 78, Fig. 2, energized, at the first interruption of each series, over a back contact of the relay 74, closes the circuit of relays 75, 76, and these relays remain energized until the series is ended. The relay 76 then releases its armatures more slowly than the relay 75, so that ground G<10> is momentarily connected over the armatures 191, 194 to the trunk wire 168. Operation of the three-wire second selector H and connector I, Fig. 3. The first set of ' vertical ' impulses energizes a relay 184 and the vertical magnet 190 to raise the wipers 205, 202, 206 to the desired level. The succeeding ' rotary ' impulse energizes a relay 195 and the private magnet 197, which moves the side switch arms 199 &c. to second position. The selfinterrupting rotary magnet 201 is now connected in and rotates the wipers 205 &c., over the bank terminals until the terminals of an idle connector 1 are reached, whereupon the side switch moves in known manner into its third position, cutting out the rotary magnet 201 and extending the trunk wires 167, 168 to the wipers 205, 206. The impulses representing the last two digits are conducted over these wipers to the connector I. The ' vertical ' impulses in the trunk wire 167 energize the relay 207, which controls first the vertical magnet 214 and then, when the side switch has moved into its second position, the rotary magnet 222. These magnets raise and rotate the wipers 242, 226, 244 so as to bring them on to the terminals of the trunk line 230, 231, which terminates in the wanted cord O<1>, Fig. 4. The rotary impulses in the trunk wire 168 energize the relay 216, which controls the private magnet 221 to move the side switch to its second and third positions. (The relay 209, energized in series with the line relays 207, 216, is at present without effect.) When the side switch moves to its third position, the arms 223, 224 extend the connexion to the trunk line 230, 231, and the arm 225 puts a guarding ground-potential on the test-terminals 227. This serves also to energize a cut-off relay 228 of the selector N belonging to the trunk 230, 231, whereby a bridge connexion through the relays 232, 233 is opened. Signalling the operator in charge of the cord O<1>, Fig. 4, and completion of the connexion to the subscriber A<1>. To signal the operator, the impulse-sender must be operated to send an extra numeral, no matter which. The connector side switch arm 215, Fig. 3, being now in its third position, the energization of the relays 207, 209 completes a circuit through the ringer relay 234. which connects the ringing-generator L<2> across the trunk 230, 231 as long as the extra impulses arrive. This energizes a relay 94, Fig. 4, which closes a circuit through a relay 96, which locks itself up and lights a call lamp 95. The relay 96 also opens the connexions between the trunk 230, 231 and the plug P<1> to prevent the current from the generator L<2> from passing through the plug P' in case the plug has not been removed from the jack of the subscriber last called. The operator replies to the call by throwing a key K<5>, which connects up her instruments S<1> and unlocks the relay 96 so as to extinguish the lamp 95. Having ascertained the number of the wanted line, the operator restores the key K<5>, completes the connexion by inserting the plug P' in the jack J', and throws the key K<6> to ring up the subscriber A<1>. Supervisory signals. The calling subscriber is supplied with microphone current through the windings of the repeater relay 74, Fig. 2, and supervisory relay 38, Fig. 1, the latter being shunted by condensers. The called subscriber is similarly supplied through the windings of the connector back-bridge relay 269, Fig. 3, and supervisory relay 92, Fig. 4. The supervisory relays 38, 92 contro